1. Field of the Invention
The present invention relates to an X-ray diffraction apparatus for detecting a diffraction X-ray diffracted from a sample by an X-ray detector when the sample is irradiated with an X-ray.
2. Description of Related Art
According to a general X-ray diffraction apparatus, a sample is irradiated with an X-ray emitted from an X-ray source while divergence of the X-ray is limited to a predetermined angle range by a divergence limiting slit (divergence slit). Diffraction of the X-ray occurs in the sample and thus a diffraction X-ray occurs from the sample when a Bragg' s diffraction condition is satisfied between the X-ray irradiated to the sample and crystal lattice planes of the sample. The diffraction X-ray emitted from the sample is detected by an X-ray detector.
In the normal X-ray diffraction apparatus, scattered X-rays occur when an X-ray emitted from an X-ray source impinges against a divergence limiting slit. The scattered X-rays cause background noise for the diffraction X-ray from the sample as a measurement target, and thus the scattered X-rays must be prevented from being incident to the X-ray detector as much as possible.
The factor causing the scattered X-rays is not limited to the divergence limiting slit. When some member exists on an X-ray optical path between the X-ray source and the sample, scattered X-rays may occur from the member.
When a detector configured to detect a diffraction X-ray in a narrow range such as a scintillation counter or the like is used as an X-ray detector, it is normal to dispose a receiving slit and an anti scatter slit (scattering slit). Scattered X-rays occurring at the divergence limiting slit are prevented from traveling by the receiving slit and the anti scatter slit to significant degree.
However, when one-dimensional X-ray detectors such as photosensor arrays or position sensitive type detectors such as PSPC (Position Sensitive Proportional Counter) or the like are arranged in a scan direction and used as an X-ray detector or when a two-dimensional X-ray detector such a CCD, a pixel detector or the like which detects a diffraction X-ray in a planarly broad range is used, it is impossible to dispose the receiving slit, the anti scatter slit or the like in front of the X-ray detector, so that scattered X-rays occurring at the divergence limiting slit are directly incident into the X-ray detector and detected by the X-ray detector. As a result, there may occur a problem that the background of measurement data increases and thus the measurement precision is reduced or scattered X-rays are erroneously detected as a peak value.
In order to overcome the background increasing problem caused by the scattered X-rays as described above, according to an X-ray diffraction apparatus disclosed in Patent Document 1 (JP-A-10-48398), an X-ray shielding member is disposed so as to confront a sample through a gap (interval) through which an incident X-ray passes. According to this X-ray diffraction apparatus, even when some member, for example, a divergence limiting slit is disposed on an X-ray optical path between an X-ray source and the sample and thus scattered X-rays or the like occur at the member concerned, traveling of the scattered X-rays or the like to an X-ray detector is obstructed by the action of the X-ray shielding member which is disposed so as to confront the sample, whereby the scattered X-rays or the like can be prevented from being taken into the X-ray detector.
Furthermore, an X-ray diffraction apparatus disclosed in Patent Document 2 (JP-A-2001-83105) is provided with not only a shielding body for shielding scattered X-rays, but also a shielding body moving mechanism for moving the shielding body to a specified position. The shielding body moving mechanism contains a Z stage which is fixed onto a surface plate independently of a goniometer, and an XY translation stage disposed on the Z stage. After the position of the shielding body is adjusted, the shielding body moving mechanism is kept at a fixed position irrespective of movement and rotation of the sample. Specifically, the shielding body can be moved in the vertical direction by the Z stage of the shielding body moving mechanism, and the movement of the shielding body is adjusted so that the center of the shielding body is coincident with the height of a primary X-ray beam (incident X-ray). Furthermore, the shielding body can be moved within a horizontal plane by the XY translation stage.
In the conventional X-ray diffraction apparatuses disclosed in the respective patent documents, each of the X-ray shielding member and the shielding body is fixed to keep a fixed relative position with respect to the sample during execution of an X-ray diffraction measurement, so that the gap through which the incident X-ray is passed is kept to be fixed.
It is originally preferable that the gap formed between the sample and the X-ray shielding member or the shielding body is adjusted in conformity with the width of an incident X-ray which is emitted from the X-ray source and whose divergence angle is limited to a predetermined angle range by the divergence limiting slit, thereby setting the breadth of the gap so that the whole incident X-ray is passed through the gap and only scattered X-rays appearing around the incident X-ray are obstructed.
When the incident angle θ of the X-ray to the sample is changed by so-called θ-2θ scan which is executed in the X-ray diffraction measurement, the width of the incident X-ray varies in connection with the change of the incident angle θ at the confronting position where the X-ray shielding member or the shielding body is disposed so as to confront the sample. Therefore, in the conventional X-ray diffraction apparatus in which the gap formed between the sample and the X-ray shielding member or the shielding body is kept fixed, the gap concerned may be smaller than the width of the incident X-ray, so that traveling of the incident X-ray is obstructed by the X-ray shielding member or the shielding body. Or, conversely, the gap concerned may be larger than the width of the incident X-ray, so that a part of scattered X-rays is passed through the gap.
The peak value of a diffraction X-ray frequently appears in a low angle region where an X-ray is incident to the sample mainly at a low angle. Therefore, it has been hitherto recognized that the gap between the sample and the X-ray shielding member or the shielding body should be adjusted in conformity with the width of the incident X-ray in the low angle region and it is less necessary for the X-ray shielding member or the shielding body to function sufficiently in a high angle region.
However, there are some materials for which the peak value of the diffraction X-ray also appears in a high angle region, and thus it has been required that the X-ray shielding member or the shielding body is made to effectively function over a broad region from the low angle region to the high angle region.